"And among those gods which ought to be placated in order to avert evil influences from ourselves or our harvests are reckoned Auruncus [from averrunco, "to avert") and Robigus."
Aulus Gellius, Attic Nights (V.12.14)
Instituted by Numa Pompilius, the Robigalia, an ancient agricultural festival celebrated in honor of Robigo (or Robigus, the gender was uncertain), the goddess of blight, red rust, or mildew, was celebrated on April 25, when the crops were most vulnerable to disease (Pliny, XVIII.285; also Varro, On Agriculture, I.1.6; On the Latin Language, VI.16). In his poem for that day, Ovid relates that he, himself, happened to meet the priest as he and his followers, all dressed in white, were on their way to the sacred grove to offer sacrifice. Joining the procession, he relates how the flamen Quirenalis carried with him the entrails of both a dog and a sheep. Incense, wine, and entrails were thrown on the fire and a prayer offered. "Scaly Robigo, god of rust, spare Ceres' grain; let silky blades quiver on the soil's skin. Let growing crops be nourished by a friendly sky and stars, until they ripen for the scythe...Spare us, I pray keep scabrous hands from the harvest. Harm no crops. The power to harm is enough" (Fasti, IV.911ff).
A similar prayer is given by Cato in his treatise on agriculture, "Father Mars, I pray and beseech thee that thou be gracious and merciful to me, my house, and my household...and that thou permit my harvests, my grain, my vineyards, and my plantations to flourish and to come to good issue, preserve in health my shepherds and my flocks, and give good health and strength to me, my house, and my household" (De Agricultura, CXLI). Here, like Robigo, the god is evoked to avert harm because he has the capacity to create it. The priest of Quirinus, a less martial aspect of Mars, also beseeches the god not to damage the crops. That there was an agricultural affinity between these deities can be seen in a passage from Tertullian, who records that "Numa Pompilius instituted games to Mars and Robigo (for they have also invented a goddess of rust)" (De Spectaculis, V).
When Ovid asked the priest why a dog had been sacrificed, he was told that it related to the rising of Sirius, the Dog Star, which coincided with the heat of summer, causing the crops to ripen prematurely. This association is probably incorrect (Sirius actually sets then) and it may be that neither Ovid nor the priest really knew the reason. Columella does speak of a young dog being sacrificed to appease the goddess (De Re Rustica, X.342ff; also Pliny, XVIII.15), and fragments from Festus (XLVIII, CCLXXXV) indicates that red dogs were sacrificed to appease the Dog Star that the corn might ripen. All are examples of homeopathic magic, where the desired event is imitated or mimicked. Here, the withering Dog Star is signified by a sacrificial dog, its color representing red rust (or the ripening corn).
This was all too much for the Christian apologist Lactantius, who had no patience with "those who regard their evils as gods, as the Romans esteem Blight and Fever" (The Divine Institutes, I.20.17). And, to be sure, a major Rogation day (from rogare, "to ask or beseech") was instituted by Pope Gregory I (died AD 604) to atone for a lack of sobriety and continence during Lent. Celebrated on April 25, the litany was intended to surplant the Robigalia.
"After, they disordered them in eating, in drinking, in plays and in lechery. And therefore our Lord was moved against them, and sent to them a great pestilence [the plague of AD 590], which was called the botche of impedimy. And that was cruel and sudden, and caused people to die in going by the way, in playing, in being at table, and in speaking one with another suddenly they died. In this manner sometime sneezing they died, so that when any person was heard sneezing anon they that were by said to him: God help you, or Christ help: and yet endureth the custom. And also when he sneezeth or gapeth, he maketh tofore his face the sign of the cross, and blesseth him; and yet endureth this custom." (Jacobus de Voragine, The Golden Legend, "The Litanies More and Lesser").
Mamertus, bishop of Vienne (died c. AD 475), had introduced three days of fasting (the minor Rogations) to beseech God's mercy during a time of disease and barbarian invasion in Gaul (Sidonius Apollinaris, Epistles, V.14.2-3, VII, 1.1-2). Before, says Sidonius, prayers "were lukewarm, irregular, perfunctory, and their fervour was destroyed by frequent interruption for refreshment; and as they were were chiefly for rain or for fine weather, to say the least of it, the potter and the market-gardener could never decently attend together!" (V.14.2). Now, the faithful fast and tearfully pray; there are sighs and bowed heads and prostrate forms. Celebrated before Ascension Day, these minor Rogations may have been intended to imitate an Ambarvalia (from ambire "to go around" and arvum "plowed or cultivated land"), the sacrifice of a pig, ram, and bull (suovetaurilia), which first were led in procession three times around the field. (There is, in fact, no specifically named Roman holiday by that name; nor is it certain that it was celebrated on May 29.)
"Above all, worship thou the gods, and bring great Ceres her yearly offerings, doing sacrifice on the springing grass close on the verge of dying winter, when now spring skies are clear. Then lambs are fat, and then wines mellowest, then sleep is sweet where the shade thickens on the hill. To Ceres let all thy rustic folk do service; to her wash thou the honeycomb with milk and soft wine, and for luck let the victim thrice encircle the springing crops and all the band of thy fellows keep it joyful company, and loudly call Ceres into the homestead: neither let any lay sickle to the ripe ears till in Ceres' praise, his brows wreathed with twisted oak, he move in rude dances and chant her hymn."
Virgil, Georgics (I.338ff, trans. MacKail)
The detail is from the Fasti Praenestini, which is in the Palazzo Massimo Alle Terme (Rome), and pertains to April 24-26. April 25 (VII Kal. Mai.) marks the date of the Robigalia. As can be read in the calendar, the grove of the deity was at the fifth milestone on the Via Claudia: Feriae Robigo Via Claudia ad milliarium V ne robigo frumentis noceat...
References: Ovid: Fasti (2000) translated by A. J. Boyle and R. D. Woodard (Penguin Classics); Cato: De Agricultura (1934) translated by W. D. Hooper and H. B. Ash; Varro: On the Latin Language (1938) translated by Roland G. Kent (Loeb Classical Library); Varro: On Agriculture (1935) translated by William Davis Hooper (Loeb Classical Library); Jacobus de Voragine: The Golden Legend (1483) translated by William Caxton. An English translation of De Verborum Significatu by Sextus Pompeius Festus has not yet been translated into English.
